This invention relates to an improved heat exchanger construction which permits substantial economies in the cost of fabricating the heat-exchanging annularly-shaped fins. The particular type of heat exchanger disclosed herein comprises a plurality of parallel fluid-carrying tubes arranged in cylindrical fashion, the tubes having a series of thin sheet metal annular fins closely spaced along their length, to enhance the heat exchanging efficiency. Each fin is provided with punched holes to receive an array of tubes. This type of heat exchanger may be mounted for rotation about the axis of the fins, with the rotation establishing an axial air flow into the center of the array and then radially outwardly over the surface of the tubes and fins. Examples of this type of heat exchanger may be found in U.S. Pat. Nos. 3,189,262 and 3,347,059. The word "annular" as used herein refers to any open-center shape, not merely purely circular rings.
To form such a fin as a single annular piece, having an inner diameter of about twelve inches, for example, would result in a substantial quantity of wasted material. In whatever pattern such fins might be arranged on a blank, considerable scrap would necessarily result between adjacent fins as well as from within the annulus.
A first step in increasing the yield from a blank would be to segment the fin, as for example, into four circumferential sections. Then such quarter-fins could be nested together on a blank, with the convex outer circumference of one segment nested in close to the concave inner diameter of an adjacent segment. However, such an arrangement still necessarily produces scrap between adjacent segments.
The invention herein disclosed completely eliminates the scrap between adjacent segments by abandoning the traditional fin configuration wherein the annulus consists of inner and outer concentric circular edges. According to the present invention, each fin is segmented, as described above, and the radius of the arc of the outer circumferential edge is made identical to the radius of the arc of the inner circumferential edge. Thus, the outer circumference of each fin takes on a lobed configuration with an outward bulge in the central portion of each fin segment. Alternative forms employ straight line rather than arcuate segments, while retaining the concept of identical inner and outer edge contours.
The result of this novel fin shape is that the fin segments can be nested perfectly on the blank, without any scrap created between adjacent segments, because the outer contour of one fin segment is identical to the inner contour of the adjacent fin segment. In this manner, the objective of more economical fabrication of the fins has been achieved.
The broad idea of shaping parts to permit line-to-line nesting on a blank is not new. It is disclosed, for example, in British Pat. No. 1553 and U.S. Pat. No. 1,416,949. While these prior art patents show the idea of nesting on a blank, neither of them suggest the essence of the present invention, namely, the abandonment of the traditional shape for an annular fin in the form of two concentric circles of unequal radii and the use instead of a segmented ring having inner and outer edges of identical contour.